Affinage

IQCB1

IQ calmodulin-binding motif-containing protein 1 · UniProt Q15051

Length
598 aa
Mass
68.9 kDa
Annotated
2026-04-28
25 papers in source corpus 10 papers cited in narrative 10 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

IQCB1 (nephrocystin-5/NPHP5) is a centriolar and ciliary transition-zone protein essential for ciliogenesis and photoreceptor outer segment formation. It directly binds CEP290 through its C-terminal region—an interaction required for ciliary gate assembly and selective cargo delivery—and maintains BBSome integrity by engaging BBS2 and BBS5 through two distinct binding sites, thereby controlling ciliary trafficking of transmembrane cargos such as smoothened and VPAC2 (PMID:18723859, PMID:23446637, PMID:25552655). IQCB1 stability and centrosomal localization are controlled by cell-cycle-regulated ubiquitination: K63-linked ubiquitination by BBS11/TRIM32 in G2/M triggers its centrosomal delocalization and cilia disassembly, while the deubiquitinase USP9X protects IQCB1 during G0/G1/S to promote ciliogenesis (PMID:28498859). Disease-causing truncating mutations abolish CEP290 binding and centrosomal targeting, and knockout in mice and dogs eliminates photoreceptor outer segments, establishing IQCB1 loss-of-function as a cause of Senior–Løken syndrome and Leber congenital amaurosis (PMID:27328943, PMID:27506978, PMID:36084637).

Mechanistic history

Synthesis pass · year-by-year structured walk · 8 steps
  1. 2008 High

    Establishing that IQCB1/NPHP5 physically and genetically interacts with CEP290/NPHP6 revealed the first direct molecular partnership at the ciliary transition zone for this gene, raising the question of what functional role this interaction serves.

    Evidence Co-immunoprecipitation with domain mapping plus synergistic zebrafish morpholino knockdown and Xenopus rescue

    PMID:18723859

    Open questions at the time
    • Whether the interaction is required for ciliogenesis was not tested
    • Subcellular site of interaction not resolved
  2. 2013 High

    Demonstrating that IQCB1 localizes to centrioles/transition zone and that its CEP290 interaction is required for an early step of ciliogenesis established IQCB1 as a core ciliogenesis factor and explained why patient truncation mutations—which abolish CEP290 binding—cause ciliopathy.

    Evidence siRNA depletion, disease-mutation functional analysis, calmodulin-binding characterization, pharmacological rescue of ciliogenesis in cultured cells

    PMID:23446637

    Open questions at the time
    • Precise step in ciliogenesis blocked by IQCB1 loss was undefined
    • Whether IQCB1 has functions beyond CEP290 binding was unknown
  3. 2014 High

    Showing that IQCB1 maintains BBSome integrity and selective ciliary cargo delivery through two distinct BBSome-binding sites expanded its role from a structural transition-zone component to a regulator of ciliary trafficking.

    Evidence siRNA depletion combined with co-immunoprecipitation and ciliary cargo localization assays for smoothened, VPAC2, and Rab8a

    PMID:25552655

    Open questions at the time
    • How IQCB1 binding maintains BBS2/BBS5 within the BBSome structurally was not resolved
    • Whether IQCB1 acts as a gatekeeper versus an assembly factor for the BBSome was unclear
  4. 2016 High

    Genetic knockout studies in mice and a canine model demonstrated that IQCB1 is essential for photoreceptor outer segment formation and function, while being dispensable for ciliogenesis in fibroblasts and kidney, establishing photoreceptor-specific vulnerability and directly modeling Leber congenital amaurosis.

    Evidence Germline knockout mouse with ERG and EM analysis; canine loss-of-function model with ERG, histology, and transcriptomics

    PMID:27328943 PMID:27506978

    Open questions at the time
    • Why photoreceptors are uniquely dependent on IQCB1 while other ciliated cells are not
    • Molecular basis of cone outer segment loss versus rod dysfunction unclear
  5. 2017 High

    Discovery that IQCB1 undergoes cell-cycle-regulated ubiquitination by BBS11/TRIM32 (K63, G2/M) and MARCH7 (K48/K63), counteracted by USP9X in G0/G1/S, revealed how cilia assembly and disassembly are coupled to cell-cycle progression through regulated IQCB1 stability.

    Evidence Co-immunoprecipitation of IQCB1 with USP9X, BBS11, and MARCH7; ubiquitin-linkage-specific assays; cell-cycle synchronization and siRNA depletion

    PMID:28498859

    Open questions at the time
    • Specific ubiquitinated lysine residues on IQCB1 not mapped
    • Whether the same ubiquitin regulation operates in photoreceptors in vivo
  6. 2019 Medium

    Localization of IQCB1 to sub-distal appendages and basal feet, and demonstration that it is required for basal foot assembly, added a second structural role distinct from its transition-zone function.

    Evidence siRNA depletion with structured-illumination microscopy and epistasis rescue in cultured cells

    PMID:31177295

    Open questions at the time
    • Finding from a single lab; independent confirmation of SDA/BF localization needed
    • Relationship between basal-foot assembly defect and BBSome/cargo trafficking phenotype unknown
  7. 2020 Medium

    Identification of EPB41L5 as a negative regulator of IQCB1 at the ciliary base—reducing its abundance and disrupting the IQCB1–CEP290 complex—provided the first upstream modulatory input controlling IQCB1 localization.

    Evidence Co-immunoprecipitation, immunofluorescence quantification, zebrafish genetic interaction

    PMID:32501287

    Open questions at the time
    • Mechanism by which EPB41L5 removes IQCB1 from the ciliary base is unresolved
    • Whether EPB41L5 regulation is relevant in photoreceptors not tested
  8. 2022 Medium

    Patient iPSC-derived photoreceptors confirmed that IQCB1 mutations reduce CEP290 protein levels and cause aberrant ciliary elongation and visual pigment mislocalization, and AAV-mediated gene augmentation rescued these defects, validating a therapeutic strategy.

    Evidence iPSC-RPE and retinal organoids from patients, Western blot, immunofluorescence, AAV rescue

    PMID:36084637

    Open questions at the time
    • Long-term efficacy and safety of AAV gene augmentation in vivo not established
    • Whether CEP290 reduction is the sole pathogenic mechanism in patient photoreceptors

Open questions

Synthesis pass · forward-looking unresolved questions
  • Key unresolved questions include why IQCB1 is essential in photoreceptors but dispensable in other ciliated cell types, what structural basis underlies its simultaneous roles at the transition zone and sub-distal appendages/basal feet, and how its ubiquitin-mediated regulation is coordinated in post-mitotic photoreceptors that lack canonical cell-cycle transitions.
  • No structural model of the IQCB1–CEP290 or IQCB1–BBSome complex
  • Photoreceptor-specific versus general ciliary function of IQCB1 not mechanistically explained
  • Ubiquitin regulation of IQCB1 not tested in post-mitotic neurons

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0060090 molecular adaptor activity 2
Localization
GO:0005815 microtubule organizing center 3 GO:0005929 cilium 3
Pathway
R-HSA-1852241 Organelle biogenesis and maintenance 3 R-HSA-9709957 Sensory Perception 3
Partners
BBS2BBS5CEP290EPB41L5MARCH7TRIM32USP9X

Evidence

Reading pass · 10 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2008 NPHP5 (nephrocystin-5) physically interacts with NPHP6 (nephrocystin-6/CEP290); the N-terminal domain of nephrocystin-6 binds nephrocystin-5, with the interacting site mapped to amino acids 696–896 of NPHP6. Synergistic phenotypes from combined zebrafish knockdown and Xenopus rescue experiments establish a genetic interaction between the two proteins in vivo. Co-immunoprecipitation/pulldown domain mapping, zebrafish morpholino knockdown (synergistic phenotype), Xenopus rescue epistasis Human molecular genetics High 18723859
2013 NPHP5 is a centriolar/transition-zone protein required for an early step of ciliogenesis. Its interaction with Cep290 is necessary for ciliogenesis, while its interaction with calmodulin (CaM) prevents NPHP5 self-aggregation. Disease-causing truncating mutations abolish Cep290 binding and centrosomal localization, thereby blocking cilia formation. siRNA depletion, co-immunoprecipitation, immunofluorescence localization, disease-mutation functional analysis, pharmacological rescue of ciliogenesis Human molecular genetics High 23446637
2014 NPHP5 contains two separate BBSome-binding sites and interacts with the BBSome to maintain its integrity; depletion of NPHP5 causes dissociation of BBS2 and BBS5 from the BBSome and loss of their ciliary localization. Cep290 (which directly binds NPHP5) additionally controls BBS8 integrity within the BBSome. Loss of individual BBSome subunits completely blocks delivery of ciliary cargos (smoothened, VPAC2, Rab8a), whereas NPHP5 or Cep290 loss selectively impairs cargo delivery. siRNA depletion, co-immunoprecipitation, immunofluorescence ciliary trafficking assays, cargo localization studies Human molecular genetics High 25552655
2016 Genetic knockout of NPHP5 in mice abolishes photoreceptor outer segment formation: Nphp5-/- photoreceptors have aberrant transition zones of reduced diameter and accumulate outer-segment transmembrane proteins in the ER. Basal bodies form but lack fully developed transition zones. NPHP5 is dispensable for ciliogenesis in mouse embryonic fibroblasts and kidney, indicating a photoreceptor-specific requirement. Germline knockout mouse, electroretinography, ultrastructural analysis (EM), immunofluorescence fractionation, EGFP-CETN2 transition-zone marker FASEB journal High 27328943
2017 NPHP5/IQCB1 undergoes cell-cycle-regulated ubiquitination: K63 ubiquitination by the E3 ligase BBS11/TRIM32 in G2/M causes NPHP5 delocalization from the centrosome and cilia loss, while K48/K63 ubiquitination by MARCH7/axotrophin (accumulated at centrosome upon USP9X loss) triggers NPHP5 degradation. The deubiquitinase USP9X is recruited to the centrosome by NPHP5 during G0/G1/S to protect NPHP5 from ubiquitination, thus promoting ciliogenesis. Co-immunoprecipitation (NPHP5–USP9X, NPHP5–BBS11, NPHP5–MARCH7), ubiquitination assays, siRNA depletion, cell-cycle synchronization, immunofluorescence PLoS genetics High 28498859
2019 NPHP5 is a novel component of sub-distal appendages (SDAs) and basal feet (BF) of centrioles/basal bodies, and is specifically required for BF assembly during ciliogenesis. NPHP5 cooperates with a subset of SDA/BF proteins in a defined hierarchical assembly pathway; loss of NPHP5 simultaneously blocks BF assembly and primary ciliogenesis, and these phenotypes can be rescued by manipulating BF assembly pathway components. siRNA depletion, immunofluorescence co-localization, epistasis by expression rescue, structured-illumination microscopy Cellular and molecular life sciences Medium 31177295
2020 EPB41L5 forms a protein complex with IQCB1/NPHP5 and regulates its localization at the ciliary base; EPB41L5 overexpression reduces IQCB1 at the ciliary base while its knockdown increases IQCB1 there. EPB41L5 also decreases IQCB1 interaction with CEP290. Genetic synergy between epb41l5 and iqcb1 in zebrafish supports their functional interaction in controlling ciliary composition. Co-immunoprecipitation, immunofluorescence localization, zebrafish genetic interaction (epistasis), zebrafish morpholino knockdown Journal of cell science Medium 32501287
2018 CNNM4 physically interacts with IQCB1; a truncated CNNM4 protein (R605X) significantly increases the CNNM4–IQCB1 interaction and increases apoptosis, functionally linking the Jalili syndrome gene CNNM4 to IQCB1. Co-immunoprecipitation, apoptosis assay with truncation mutant Molecular genetics and genomics Low 29322253
2022 In patient-derived iPSC-RPE and retinal organoids with IQCB1/NPHP5 mutations, CEP290 protein levels are reduced, providing a plausible mechanism for aberrant ciliary gating; patient cells show aberrantly elongated ciliary axonemes and impaired outer segment development with visual pigment mislocalization. AAV-mediated IQCB1 gene augmentation rescues these defects. iPSC differentiation (RPE, retinal organoids), immunofluorescence, Western blot (CEP290 levels), AAV rescue Stem cell reports Medium 36084637
2016 In the canine NPHP5-LCA model, rod and cone photoreceptors form a sensory cilium but develop and function abnormally and rapidly degenerate; cone outer segments are absent, indicating ciliary dysfunction. Rod- and rod/cone-expressed genes are significantly downregulated while cone-specific genes are unchanged, and cell-death/survival pathway genes are downregulated. Canine loss-of-function model, ERG, histology, comparative gene expression profiling Human molecular genetics Medium 27506978

Source papers

Stage 0 corpus · 25 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2011 Cone photoreceptors are the main targets for gene therapy of NPHP5 (IQCB1) or NPHP6 (CEP290) blindness: generation of an all-cone Nphp6 hypomorph mouse that mimics the human retinal ciliopathy. Human molecular genetics 102 21245082
2011 IQCB1 mutations in patients with leber congenital amaurosis. Investigative ophthalmology & visual science 95 20881296
2014 Nephrocystin proteins NPHP5 and Cep290 regulate BBSome integrity, ciliary trafficking and cargo delivery. Human molecular genetics 75 25552655
2008 Genetic and physical interaction between the NPHP5 and NPHP6 gene products. Human molecular genetics 67 18723859
2013 Pathogenic NPHP5 mutations impair protein interaction with Cep290, a prerequisite for ciliogenesis. Human molecular genetics 60 23446637
2011 Variations in NPHP5 in patients with nonsyndromic leber congenital amaurosis and Senior-Loken syndrome. Archives of ophthalmology (Chicago, Ill. : 1960) 55 21220633
2011 Whole-exome sequencing identifies ALMS1, IQCB1, CNGA3, and MYO7A mutations in patients with Leber congenital amaurosis. Human mutation 53 21901789
2016 Overlap of abnormal photoreceptor development and progressive degeneration in Leber congenital amaurosis caused by NPHP5 mutation. Human molecular genetics 40 27506978
2013 IQCB1 and PDE6B mutations cause similar early onset retinal degenerations in two closely related terrier dog breeds. Investigative ophthalmology & visual science 39 24045995
2017 USP9X counteracts differential ubiquitination of NPHP5 by MARCH7 and BBS11 to regulate ciliogenesis. PLoS genetics 35 28498859
2016 Ciliopathy-associated IQCB1/NPHP5 protein is required for mouse photoreceptor outer segment formation. FASEB journal : official publication of the Federation of American Societies for Experimental Biology 34 27328943
2021 Gene therapy reforms photoreceptor structure and restores vision in NPHP5-associated Leber congenital amaurosis. Molecular therapy : the journal of the American Society of Gene Therapy 29 33781914
2022 In vitro modeling and rescue of ciliopathy associated with IQCB1/NPHP5 mutations using patient-derived cells. Stem cell reports 26 36084637
2017 Early-Onset Progressive Retinal Atrophy Associated with an IQCB1 Variant in African Black-Footed Cats (Felis nigripes). Scientific reports 19 28322220
2018 Identification of a mutation in CNNM4 by whole exome sequencing in an Amish family and functional link between CNNM4 and IQCB1. Molecular genetics and genomics : MGG 15 29322253
2020 Transient pupillary light reflex in CEP290- or NPHP5-associated Leber congenital amaurosis: Latency as a potential outcome measure of cone function. Vision research 13 32088401
2018 Rescue of cone function in cone-only Nphp5 knockout mouse model with Leber congenital amaurosis phenotype. Molecular vision 12 30713422
2019 Requirement of NPHP5 in the hierarchical assembly of basal feet associated with basal bodies of primary cilia. Cellular and molecular life sciences : CMLS 8 31177295
2013 Clinical features and mutation of NPHP5 in two Chinese siblings with Senior-Løken syndrome. Nephrology (Carlton, Vic.) 8 24674142
2011 Senior-Loken syndrome secondary to NPHP5/IQCB1 mutation in an Iranian family. NDT plus 5 25984213
2024 IQCB1 (NPHP5)-Retinopathy: Clinical and Genetic Characterization and Natural History. American journal of ophthalmology 4 38522724
2020 Epb41l5 interacts with Iqcb1 and regulates ciliary function in zebrafish embryos. Journal of cell science 3 32501287
2025 Long-read technologies identify a hidden LINE-1/ERV1 insertion in IQCB1 as causative variant for Senior-Løken syndrome. NPJ genomic medicine 1 40263280
2025 A Novel NPHP5 Gene Mutation in Three Siblings With Nephronophthisis Without Retinitis Pigmentosa: A Case Report. Case reports in genetics 0 40331022
2025 Senior-Løken syndrome with IQCB1/NPHP5 mutation in an adult: a case report. Journal of medical case reports 0 41316455